OPGW Installation Procedure

PURPOSE

Describe the system of installation and delivery of OPGW fibre optic cables.

GENERAL

In general, the system and the equipment used for installation of the OPGW are similar to those of the standard ground wire cable.

Nevertheless, there is an optical fibre core, fibres should be protected from suffering any damage by observing the minimum bending radius at all times. Therefore, specific components and machinery are used for the OPGW cable: pullers, tensioners, anti-twisting counterweights, swivels, pulling grips, pulley-blocks, self-gripping clamps, pulling ropes, pulling cables, etc.

PROCEDURES

Survey of the line

Prior planning for installation of the OPGW cable is performed by monitoring the line, taking into account the following parameters:

Length of each drum

The OPGW drum length is determined based on the following considerations: position of the tension towers, tower access, distance between supports and crossing with other lines, roads, railways, routes, services and other obstacles.

Splices

The position of the splices depends on the maximum available length of OPGW, on the position of the towers and the tower access.

Transport, loading, unloading and storage

The following procedures are recommended to prevent the cable from suffering damage during handling, transport and storage:

1. The drums should always be transported in vertical position with the cable ends fixed to prevent cable from slackening. All of the staves and safeguards should be maintained until the drums are situated for immediate installation.
2. After the transport, the drums should be inspected to verify that they have not been damaged and that none of the staves or safeguards is broken.
3. The drums should never, in any case, be thrown from the lorry during unloading, or moved by uncontrolled rolling.
4. Loading and unloading are performed so that the drum remains in vertical position and the sides of the drum are not damaged.
5. The drums can be moved by rolling a short distance ensuring that there are no objects that may damage the staves. The direction the drum turns should follow the instruction of the mark on the drum.
6. In any case the drum should not be stored horizontally.
7. The ends of the cable should be sealed to prevent water penetration.
8.  The drums should be stored on flooring that is strong enough to avoid sinking.
9. The drums should be stored to facilitate handling and loading, and should be located on a safe place where they will not be damaged.
   

Preparation for installation

Positioning the equipment

Drum

The drum is placed at the selected site (with the space required for its location) so that the cable outlet is on the upper part and aligned with the planned laying direction.

The drum must be located at a distance of 2 or 3 metres from the tensioner. The lifting components usually used are hydraulic jacks and a bar with the suitable dimensions inserted in the central opening of the drum.

The drum must be located at a height of 10 to 15 cm from the ground.

Puller and tensioner.

Either the puller or the tensioner must be placed at a minimum distance from the tower equal or more than twice of the tower’s height.

The tensioner as well as the puller should be placed aligned with the conductors. The maximum acceptable deviation angle is 30º. (< 30º)

If it is not possible to achieve this angle, the puller and tensioner are placed close to the following tower, using an additional pulling cable of the required length. At 90º or less angle, retracking of the optic cable is not allowed. The tensioner as well as the puller should be positioned at a minimum distance equivalent to twice the height of the support to which the cable is fastened. In the installation with retracking, the smallest angle must be more than 90º and the final pulley should be placed at a distance equal to twice of the tower’s height. In the tensioner, the first groove that the cable will pass through must be perpendicular to the axis of drum. The tensioner must be equipped with a dynamometer (i). Its reels must be protected with material that does not damage the outer layer of the OPGW cable. The puller must also be equipped with a dynamometer 1(i), with automatic disconnection in case of over tension on the cable. The pulling cable should be joined to the OPGW cable by a swivel and a pulling grip. The minimum diameter of the reels (where the OPGW is to be coiled) used during the installation should be at least 80 times the diameter of the OPGW cable. For example, the tensioner reels for a 15 millimeters cable should have a diameter of approximately 1.2 metres. Either the braking device or the puller has to be suitably connected to the ground by a system of moveable rollers such as that shown in the following picture. This also applies to the OPGW cable and the pulling cable, if it is a metal one.

Pulleys

The tower pulleys should have a minimum diameter of at least 0.8 metres in the following cases:

- In all towers with a change in laying direction equal to or greater than 15 degrees.

- In the first and in the last tower of a single installation.

- If the distance between the towers is greater than 600 metres.

In all the other cases pulleys with a diameter of 0.6 m can be used.

The pulleys have to be under good use conditions. The pulley groove should be protected with neoprene or other similar material.

In case of sharp angles, the pulley must be placed so that the cable always passes through the centre of the groove

If the angles are greater than 30 º, a dual pulley system must be used in order to increase the bending radius during the installation. The diameter of each pulley should be at least 0.6 m

Anti-twisting devices

When a single or double layer OPGW cable is installed, an anti-twisting device is required to compensate the inherent effect of torque of the OPWG cable. This device is always positioned at the pulling head of the

OPGW cable and equipped with two counterweights placed at a distance that is at least 3 meters one from the other. In this way that when one counterweight goes through the pulley the other is operative.

Another anti-twisting device is installed at the end of the OPGW cable just before it leaves the tensioner.

The weight of the anti-twisting devices has to be high enough to prevent OPGW cable rotation. The minimum values recommended for each counterweight are as follows:

- Spans 300 m 12 kg

- Spans 300 m - 700 m 15 kg

- Spans 700 m 20 kg

For Installation length longer than 4000 metres these values should be increased by 5 kg.

After the counterweights have been installed, they should not be removed until the cable is secure and cannot rotate.

Special precaution must be taken so that the cable does not rotate inside the counterweights, due to unsuitable cable dimensions or incorrect tightening.

Auxiliary components

The swivel is specifically designed for OPGW cables. They are of the suitable size for the cable to beinstalled and in optimum condition for use

The pulling grip for OPGW cable stringing must be at least 1.5 metres long and specifically designed for stringing OPGW cables. Moreover, it should be of the suitable dimensions and in optimum condition for use.

The clamps used during stringing operations have to be specifically designed for OPGW cables and must be suitable for the OPGW cable diameter.

If preformed fittings are used, these should be specifically designed for the OPGW cable to be installed. The diameter as well as the length and material of these components must be suitable for the OPGW cable.

The torque wrenches used must be reliable and calibrated on a regular basis. If a fall or accidental damage occurs, the calibration must be verified.

Pulling rope

The pulling rope has to be specifically designed for cable stringing. As stringing is performed on a power line that is out of service we recommend the rope to be a metallic one. The minimum breaking load must be 5000 kg. This value can be higher depending upon the OPGW cable mechanical characteristics and at least equal to 2.5 times the maximum stringing load. If an old earth cable must be used as a pulling rope, ensure that it is not damaged and that its weight is lower than the OPGW cable one that is going to be installed. The pulling cable must be joined to the optical cable by a swivel and a pulling grip. The swivel is necessary to prevent any twisting of the cable when stringing is performed. As a rule, one drum at a time of OPGW cable is installed.

Installation of OPGW

Important factors to be taken into account during stringing

Basic controls

Strict controls must be established during installation to ensure that it is performed correctly, without excess tension, twist of the OPGW, unsuitable compression, regulating a correct sagging. Neither the fibres nor the tube will be damaged.

The tensioner and the puller should be placed at a distance from the first tower pulley which is equivalent to at least twice the height of the pulley.

Intermediate control points should be established, with the necessary precautions that are required at critical points during installation (beginning/end of drum, angles, etc.).

During installation, the OPGW cable should not strike nor graze any objects other than the pulleys. No obstacles must prevent the pulleys from rotating in the correct way.

The minimum bending radius must be controlled during all installation operations.

Ensure that the metal part of the pulleys do not make contact with the cable to prevent it from being  damaged.

Stringing speed

The maximum permissible stringing speed is 40 metres per minute. It always depends on the stringing conditions and must be reduced to avoid damages to the optical fibres, the tube and the OPGW cable.

Pulling tension

The recommended pulling tension shall be lower than 1.5 times the weight (kg) of 1 km OPGW cable length.

In case that higher pulling tensions are required, further information should be asked to ZHC supervisor in order to know the maximum permissible pulling tension for such particular installation.

Minimum bending radius

The minimum bending radius is as follows:

- on tensioner reels 40 times the cable diameter

- during installation 400 mm

- after installation 20 times the cable diameter

Communications during stringing

The personnel located at the puller, the tensioner, the pulley crossings and the cable ends are in communication at all times by communication system.

Sagging of the cable

Generally, the methods used to obtain the correct sag values of the OPGW cables are the same used for conventional ground wire cables. The specific recommendations are as follows:

Pulling is performed by a preformed fitting or tension clamp (in intermediate spans) or with the pull jacket at the end.

Sagging of the cable and fittings installation are always performed after stringing. At this time, the attachment fittings are also installed to prevent damage to the OPGW cable.

The installer is responsible for any damage to the OPGW cable that may occur due to failure cause by incorrect application of the previous points.

If the tension and sags are different from the expected values, the stringing or sagging should be halted.

The Zhongtian Hitachi supervisor and the project leader will be consulted in order to safely continue the installation operations.

Installation of fittings and accessories

The fittings: tension clamps, suspensions, earthing clamps, dampers, etc. should be installed in accordance with the manufacturer’s instructions and using the appropriate tools.(see part 5)

Personnel training

All personnel who participate in the installation of the OPGW cable should be informed of handling problems and installation procedures for the OPGW cable.